Knowledge Bank

The $N=1\to 1$ and $ N=1\rightarrow2$ rotational transitions of CD, and the $N=1\to 1$ lines of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$CH have been measured in their $2\Pi r$ ground electronic states using sub-mm direct absorption spectroscopy. The measurements below 600 GHz (CD: $N=1\to 1$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$CH: $N=1\to 1$) were carried out at Arizona, while those in the 900 GHz range were conducted at JPL (CD: $N=1\to 1$). The two radical species were created in an electrical discharge of either $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$CH$4$ or CD$4$. Both lambda-doubling and hyperfine splitttings were resolved in the spectra. The data were analyzed with a case(b) effective Hamiltonian, resulting in an improvement in the lambda-doubling and deuterium, proton, and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$C hyperfine constants. Highly accurate rest frequencies are now available for astronomical searches for these species. CH is an abundant and widespread interstellar molecule, and thus CD and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$CH should be of astrophysical interest.